The present invention relates to a system for anaerobically digesting manure and other materials, and more particularly to a digester for use in an anaerobic digesting system.
Animal manures and other organic materials are digested anaerobically, that is, in the absence of oxygen, to detoxify the materials to make them safe for disposal or secondary use. By-products of the anaerobic digestion system are methane and single cell protein.
Organic feed stock, such as manure, is introduced into digesters in the form of thick aqueous slurries. If allowed to stagnate in the digester, the slurry separates into a heavy phase, a liquid phase and a light phase. The heavy phase settles out and cemented by the action of anaerobic bacteria into a monolithic block on the bottom of the digester. The light phase rises to the top of the liquid phase. The light phase is usually high in fiber so that the anaerobic bacteria glues into a composite mat of considerable strength, forming a film over the top of the liquid phase. Once the heavy and light phases have been allowed to form and solidify, it is difficult to break up the build up in the digester and to remove the heavy and light phases.
Mechanical agitators have been employed to maintain movement of the heavy phase. The mechanical agitators are subject to corrosion and breakage because of the severe environmental conditions at the bottom of the digester. Accordingly, mechanical agitation is not the final answer. Regarding the light phase, no satisfactory solution has been suggested for prevention of formation of the fibrous mat.